I have a j-340 240 volt tub.
The circulation pump is running, the heater light is on but the heater will not work. So far here is what I have.

The heater input at the board measure 230 volts ( across both terminals)
The heater output measures 30 volts ( across both terminals).
Unplug the heater output terminals and measured at the circuit board spades 30 volts.

The heater element reads 0.50 ohms on a 20k setting on meter.

Circuit board terminal for the heater output has a small amount of black smoke on then connection..